Provo, Utah — It will take something of a political coup to oust three-term UtahRepublican Sen. Robert Bennett, but that's exactly what his opponents have been busily orchestrating.

These aren't Democrats plotting against Senator Bennett, one of the country's most conservative lawmakers. These are Republicans – more precisely, "tea party" Republicans, who say Bennett just isn't conservative enough.

Their plan to keep him from returning to Washington may work. In two recent surveys of Republican delegates, who vote at a May 8 convention on whom they want the Senate nominee to be, Bennett trailed far behind Mike Lee, an attorney who once clerked for Supreme Court Justice Samuel Alito and who has become a favorite among many tea partyers.

"There is more anger toward Washington, more anti-incumbent feeling than I have seen in years," says LaVarr Webb, a veteran political consultant and former journalist in Utah. "That, of course, is all bad news for Bob Bennett."

While tea partyers are perhaps best known for directing their discontent over taxes, deficit spending, bailouts, and health-care reform at President Obama and his Democratic allies, incumbent Republicans – sometimes seen as too moderate, or as part of the Washington machine – are also in their sights.

Riding a new wave of antiestablishment sentiment, spread via Twitter and Facebook and fueled by conservative talk radio, candidates who speak the language of the tea partyers are mounting serious primary challenges to mainstream Republicans in Florida, Kentucky, and Indiana.

The outcome of these votes will define the clout, or lack thereof, of the fledgling tea party movement, says Jennifer Duffy, senior editor for the Cook Political Report. "They will get a lot of mileage if they manage to deny the nomination to Bennett, who, the last time I checked, is no raving moderate."

Though Bennett has well-established conservative credentials (he supports gun rights and favors tighter immigration controls), many tea partyers, as well as the antitax group the Club for Growth that is campaigning against Bennett, cite his 2008 vote in favor of the Troubled Asset Relief Program (TARP) bank bailout as the thing that put him on the wrong side of their movement.

"The common thread through all of this is fiscal responsibility," says David Kirkham, who organized Utah's first tea party protest on March 6, 2009. "I want to turn back to constitutional principles."

Since that first rally that drew about 100 people to the state capitol building in Salt Lake City, Mr. Kirkham has helped organize more than a dozen other protests. The most recent one, on April 15, drew about 1,300 people.

While Utah may not be the epicenter for the grass-roots tea party movement (Utah is, after all, already one of the more conservative states), it may be the place where its political impact is most immediately realized. And that's largely due to the state's unique political system.

In Utah, candidates are selected at party nominating conventions, giving activists the upper hand in determining who ends up on the ballot. At the Utah Republican Convention in Salt Lake City, 3,500 delegates will vote on seven contenders for the Senate nomination. If one candidate gets 60 percent of delegates after three rounds of voting, he or she becomes the GOP nominee, skipping a primary and going straight to the general election to face the Democratic candidate. (Democrats also have a convention May 8.) If no candidate captures the coveted 60 percent, the two lead contenders face off in a June primary.

The trouble for Bennett, according to an April poll commissioned by the Deseret News and Utah's KSL-TV, is that 41 percent of delegates say they are dead set against voting for him. That would suggest that the best-case scenario for Bennett would be a runoff with Mr. Lee, who is leading in the same poll with 31.2 percent of the delegate support, or Tim Bridgewater, a businessman who has 17 percent.

While the tea party remains a loosely organized group that is not endorsing any single candidate, both Lee and Mr. Bridgewater have their share of support among Republican activists.

"There are a lot of unhappy delegates," says Kirkham, who, like about 70 percent of the delegates this year, will attend the convention for the first time. Many of the newcomers have been chosen by their neighborhood precincts specifically for their anti-Bennett stance, he says, as well as their tea party credentials. According to a Salt Lake Tribune poll, 68 percent of delegates say they are tea party supporters.

In many ways, Kirkham reflects the face of the tea party movement both in Utah and nationwide: He's never voted in a primary election before. Until recently, he wasn't registered to one party or another. He's a political neophyte. But this newly active Republican, who has become one of about 10 unofficial tea party leaders in Utah, is suddenly influential.

On a recent Monday afternoon at his Provo company that builds replicas of vintage sports cars, Kirkham checked his Gmail in-box. It was filled with e-mails from candidates and tea party activists.

Bennett has acknowledged that anti-incumbent sentiment among party activists is making his reelection bid tougher, but he says that many delegates remain undecided. "The only real conclusion we can come to is that the race is still very volatile and people are changing their minds," Bennett recently told The Salt Lake Tribune.

He has enlisted the aid of Mitt Romney, the former Massachusetts governor and Republican 2008 presidential hopeful, who, as a Mormon, is widely popular in Utah. Mr. Romney has defended Bennett's support for TARP and will introduce him at the state Republican convention in a bid to sway undecided delegates.

If one state allows party activists to make a point, it's Utah, says Ms. Duffy, who tracks congressional campaigns around the country. And while the tea party's momentum may be more exaggerated in Utah because of the convention process, it may nonetheless spell the end of Bennett's 18-year Senate career.

"If Bennett does not make it into the primary, while the tea party is thrilled with the results, Congress may not be better off for it. Bennett is one of these guys who is well liked on both sides of the aisle," she says.

As the tea party emerges in Utah, many moderate Republicans are feeling marginalized. Delegates tend to be much more conservative on key issues than average Republican voters. Utah's process is giving the tea party a louder voice, but if Republicans are unhappy with that direction, they should get involved, says Mr. Webb, the Utah political analyst who is also a convention delegate.

"Clearly the battle for the heart and soul of the Republican Party is going on, and I don't think anyone has emerged the winner," he says. "If you're a conservative, there are plenty of things to be upset about. It's a tough time for incumbents."